A new technique in NMR may offer diffraction limited resolution.

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Nuclear Magnetic Resonance (NMR) has probably been the most fertile ground in physics since the early 1950s. In every decade since its discovery there has been at least one and often two discoveries made with NMR that have been of enough significance to be deserving of a Nobel prize and the end is not yet in sight. The thing that drives NMR to great heights is its versatility; from the unambiguous identification of complex organic molecules to determining the three-dimensional structure of proteins and imaging the brain, NMR can do it all. Probably the biggest hindrance to making new discoveries with NMR today is the relatively poor spatial resolution.

Optical microscopes have great resolution, but lack the versatility — in fact, direct chemical imaging of various flavors doesn't even come close to NMRs ability to identify complex organic molecules, and florescence labeling works mainly when you already know what to look for. What is really needed is a mechanism to combine NMR with optical microscopy into a super-magnificent imaging technique. Now the first steps towards such a combination have been taken. The researchers make use of the fact that light passing through a magnetic field has its polarization rotated slightly. This effect, called the Faraday effect, is enhanced when all the nuclear magnetic spins are lined up, which is exactly what NMR does to obtain its signal. However, instead of detecting a radio frequency signal as the spin decays, the researchers observe the change in the amount of rotation. This has been done before in dilute metallic gases and special systems like quantum dots, but what makes this special is that the researchers have measured this by looking at the hydrogen proton spins in ordinary water, which is a huge step towards making the technique useful.

I should note that the rotation is very slight and their signal to noise ratio wasn't that great, so they had to average for 20 minutes or more to get good data. For a first demonstration of the technique this is a fantastic result because, as the authors point out, there are several obvious and relatively easy improvements that can be made to the apparatus. The potential for this technique cannot be overstated. For example, adding a few optics and a CCD turns this into a microscope with the selectivity of NMR. Or add a tunable laser and gain all the benefits of optical spectroscopy in parallel with those of NMR. Did I just hear some biochemists' heads explode?

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Chris Lee
Chris writes for Ars Technica's science section. A physicist by day and science writer by night, he specializes in quantum physics and optics. He Lives and works in Eindhoven, the Netherlands. Emailchris.lee@arstechnica.com